help				Show help.
db.help()			Show help for database methods.
db.<collection>.help()	Show help on collection methods. The <collection> can be the name of an existing collection or a non-existing collection.

// create
use <db>			// Switch current database to <db>. The mongo shell variable db is set to the current database.

// Get 
show dbs			// Print a list of all databases on the server.
show databases		// New in version 2.4: Print a list of all available databases.
MongoClient -> getDatabaseNames()

show collections	// Print a list of all collections for current database
show users			// Print a list of users for current database.

// drop database
db.dropDatabase() // Removes the current database
DB -> dropDatabase()